Color developers containing color developing agents of the aromatic primary amine type have been used from of old for formation of color images and at present have a primary role in the color photographic image-forming process. However, the color developers described above are exceedingly prone to air oxidation and oxidation due to the presence of. It is well-known that when color images are formed using oxidized developing solutions, an increase in fog density and changes in photographic speed and gradation are caused, which interfere with achieving the intended photographic characteristics.
Therefore, various means for enhancing preservability of color developers have so far been investigated. The most general means among them is the combined use of hydroxylamine and sulfite ion. However, this method has the drawback that the hydroxylamine produces ammonia by decomposition which causes fog and the sulfite ion competes against the developing agent to impair developability. Accordingly, it is hard to say that both of them are preferred as a compound capable of enhancing the preservability of a color developer (or a preservative).
In particular, sulfite ion, though it has been used from of old as an agent capable of increasing the preservability of various color developing agents or preventing the decomposition of hydroxylamines, drastically impairs developability and lowers color density of the developed image to a considerable extent, especially when it is used in a system free of benzyl alcohol. Benzyl alcohol is harmful from the standpoint of environmental pollution and preparation of developers.
Alkanolamines described in Japanese Patent Application (OPI) No. 3532/79 (the term "OPI" as used herein means an "unexamined published application") and polyethylene imines described in Japanese Patent Application (OPI) No. 94349/81 have been proposed as a substitute for sulfites. However, these compounds cannot produce sufficient effects.
In addition, various kinds of preservatives and chelating agents have been examined for the purpose of improving the stability of color developers.
As examples of preservatives, aromatic polyhydroxy compounds described in Japanese Patent Application (OPI) Nos. 49828/77, 160142/84 and 47038/81, U.S. Pat. No. 3,746,544, and so on, hydroxycarbonyl compounds described in U.S. Pat. No. 3,615,503 and British Pat. No. 1,306,176, .alpha.-aminocarbonyl compounds described in Japanese Patent Application (OPI) Nos. 143020/77 and 89425/78, metal salts described in Japanese Patent Application (OPI) Nos. 44148/82 and 53749/82, hydroxamic acids described in Japanese Patent Application (OPI) Nos. 27638/77, and so on, may be mentioned.
As examples of chelating agents, on the other hand, mention may be made of aminopolycarboxylic acids described in Japanese Patent Publication Nos. 30496/73 and 30232/69, organic phosphonic acids described in Japanese Patent Application (OPI) No. 97347/81, Japanese Patent Publication No. 39359/81 and West German Pat. No. 2,227,639, phosphonocarboxylic acids described in Japanese Patent Application (OPI) Nos. 102726/77, 42730/78, 121127/79, 126241/80 and 65956/80, and so on, and other compounds described in Japanese Patent Application (OPI) Nos. 195845/83 and 203440/83, Japanese Patent Publication No. 40900/78, and so on.
However, sufficient preservability cannot be obtained with any of the preservatives and chelating agents described above and, what is worse, some of them exert undesirable effects upon photographic characteristics.
For the foregoing reasons, satisfactory results have not yet been achieved and the advent of excellent preservatives, especially those capable of taking the place of sulfites, have been desired.
Further, it is described in Japanese Patent Application (OPI) Nos. 95345/83 and 232342/84 that a color photographic material comprising a silver chlorobromide emulsion with a high chloride content tends to generate fog at the time of color development. When an emulsion of the above-described kind is used, a preservative which has low solubility in the emulsion and more excellent preservability is essential to a color developer. Any preservative which will suffice for the above-described needs also has not been found until now.